GSM/EDGE Radio Access Network, GERAN, is a term given to the Global System for Mobile communications, GSM, radio access technology, including its evolutions in the form of Enhanced Data rates for Global Evolution, EDGE, and for most purposes, the General Packet Radio Service, GPRS.
General Packet Radio Service (GPRS) provides mobile users access to value-added services and different external packet switched networks. These networks can be, for example, the Internet or corporate intranets. The Base Station Subsystem (BSS) of the Global System for Mobile Communications (GSM) network provides the radio interface to mobile stations (MS) via the Base Transceiver Station (BTS) and a network interface to the GPRS core network. The GPRS core network handles mobility and access to external packet networks and services.
The GPRS core network is the central part of the general packet radio service (GPRS) which allows Universal Mobile Telecommunications systems (UMTS) mobile networks to transmit Internet Protocol (IP) packets to external networks such as the Internet. The GPRS is an integrated part of the GSM network switching subsystem and acts in parallel with the GSM network, providing packet switched connections to the external networks. One of the requirements of a GPRS network is that it must be able to support different Quality of Service (QoS) subscriptions of the user.
FIG. 1 shows a simple block diagram over the architecture of a GPRS network. The GPRS system has some new network elements compared to an existing GSM network. Some of these elements are GPRS Support Nodes (GSN) which are network nodes supporting the use of GPRS in the GSM core network. The Gateway GPRS Support Node (GGSN) 400 is responsible for the interworking between the GPRS network and external packet switched networks, like the Internet. The Serving GPRS Support node (SGSN) 300 corresponds to the Mobile Switching Center (MSC) 500 in a GSM network and is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. The GGSN converts the GPRS packets coming from the SGSN into the appropriate Packet Data Protocol (PDP) format and sends them out on the corresponding packet data network. In the other direction, PDP addresses of incoming data packets are converted to the GSM address of the destination user. The readdressed packets are sent to the responsible SGSN.
The BSS 250 is responsible for handling traffic and signalling between a mobile station (MS) 10 and the network switching subsystem. The BSS comprises a Base Transceiver Station (BTS), for example a Radio Base Station (RBS) 100 which contains transceivers, antennas, and equipment for encrypting and decrypting communications with the Base Station Controller (BSC) 200. The BSC classically provides the intelligence behind the BTSs and handles allocation of radio channels, receives measurements from the MSs, and controls handovers from BTS to BTS.
The GPRS system introduces new interfaces to the GSM network. For example, the Gb interface connects the BSS to the SGSN in the GPRS core network and carries the GPRS traffic and signalling between the GSM radio network (BSS) and the GPRS network, the Abis interface is the interface between the BTS and BSC, and the Gn interface is an interface between two GSN nodes and supports the GPRS tunneling protocol.
The Packet Data Protocol (PDP) context is a data structure present on both the SGSN and the GGSN and contains the subscriber's session information when the subscriber has an active session. When a mobile station (MS) wants to use GPRS, it must first attach and then activate a PDP context. This allocates a PDP context data structure in the SGSN that the subscriber is currently visiting and the GGSN serving the subscriber's access point.
Differentiated Services of DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing QoS on modern IP networks. DiffServ can, for example, be used to provide low-latency to critical network traffic such as voice or streaming media while providing simple best-effort service to non-critical services such as web traffic or file transfers. DiffServ uses the 6-bit Differentiated Services Field (DS field) in the IP header for packet classification purposes.
DiffServ operates on the principle of traffic classification, where each data packet is placed into a limited number of traffic classes, rather than differentiating network traffic based on the requirements of an individual flow. Each router on the network is configured to differentiate traffic based on its class. DiffServ-aware routers implement Per-Hop Behaviors (PHBs), which define the packet-forwarding properties associated with a class of traffic. Different PHBs may be defined to offer, for example, low-loss or low-latency. The PHB is determined by the DS field of the IP header. The DS field contains a 6-bit Differentiated Services Code Point (DSCP) value.
As schematically illustrated in FIG. 2, the MS sends a request to the SGSN for a certain level of QoS in a PDP Context Activation Request for each connection the MS want to use. Actual attributes and parameters are then subject to a negotiation procedure between the BSS (BSC) and the SGSN (Aggregate BSS QoS Profile (ABQP) procedures) based on the traffic type demanded by the end-user application and available resources. As a result, a QoS profile is created for the certain traffic class and appropriate resources (like, for example, Packet Data Channels (PDCHs)) are reserved for the air interface by the BSC. QoS attributes within the PDP contexts for each connection of a user application are stored in both the MS and in the GSN.
In case of legacy, non-IP BTSs, the actors of this process are the SGSN, BSC and the MS. At the end of the process, the MS is notified if the PDP context is accepted and what QoS Profile has been negotiated.
Each MS may have several Packet Flow Contexts (PFCs) associated with it, depending on the number of active PDP contexts and the QoS profile of each PDP context. Each PFC is identified by the Packet Flow Identifier (PFI) which is assigned by the SGSN. For each MS, the BSS will store the ABQPs for the PFCs of that MS and the ABQP may then be addressed via the PFI, if the MS supports this.
PFI is signaled within the Radio Link Control (RLC) Uplink Data Block. PFI itself cannot identify the traffic type since the same traffic class may use different PFI values according to the fact that these flows may belong to different PDP contexts.
The IP Radio Access Network (RAN) transport network (Abis interface) and the core network (Gb interface) are not aware of what the QoS is of the traffic they actually carry. Thus all traffic types over the (E)GPRS service may be considered as the same and classified as the same Differentiated Services (DiffServ) Per Hop Behaviour (PHB).
The technical specification of Radio Link Control/Medium Access Control (RLC/MAC) protocol for GPRS over the MS-BSS interface is described in detail in 3GPP TS 44.060: General Packet Radio Service (GPRS), Mobile Station (MS)-Base Station System (BSS) interface, Radio Link Control/Medium Access Control (RLC/MAC) protocol.
In the past, the radio interface was considered to be a bottleneck. Current QoS architecture provides a solution to overcome this technical barrier. However, due to the expected increase in traffic from future all-IP multistandard sites, QoS comes even more in focus. Now, it is important that data traffic irrespective of whether generated by LTE, WCDMA or GSM will receive the same handling over the IP networks.
Streaming applications generate the major part of data traffic in cellular networks. Streaming may not only be a simple file download. Inelastic traffic is sensitive to delay and jitter. Without proper traffic management it is impossible to meet these requirements.
According to current trends, (E)GPRS services will take part more and more in serving the continuously increasing data traffic.
Thus, it would be desirable to provide improvements related to data traffic management in a wireless communication network, in particular an (E)GPRS network.